Method of producing a gel containing concentrated sulfuric acid

ABSTRACT

Method of producing a gel containing concentrated sulfuric acid for use in lead accumulators having dry storagable charged electrode plates comprising polymerizing acrylic acid, methacrylic acid or amides thereof in solution with cross-linking agents, grinding the resultant gel, drying the ground gel and thereafter soaking the resin particles thereby obtained in concentrated sulfuric acid.

I United States Patent 91 [111 3,765,950 Lauck 1 1 Oct. 16, 1973 [54]METHOD OF PRODUCING A GEL 2,684,950 7/ 1954 Rivers et al 252/317CONTAINING CONCENTRATED SULFUR: 3,408,233 10/1968 Parker et a1. 136/153ACID 3,419,430 12/1968 Michaels 136/157 3,556,851 1/1971 Douglas et a1.136/157 [75] Inventor: Helmut Lauck, Schlobborn, 3,586,539 6/1971 Lauck136/158 Germany [73] Assignee: Varta Aktiengesellschaft, Frankfurt OTHERPUBLICATIONS am Germany Roth et a1., Defensive Publication T863,007,Pub- [22 Filed: June 9, 1972 i e June 2 1969.

[21] Appl. No.: 261,162

Related US. Application Data Continuation-impart of Ser. No. 16,931,March 5, 1970, abandoned.

Primary ExaminerD0nald L. Walton Att0meyMichae1 S. Striker Method ofproducing a gel containing concentrated sulfuric acid for use in leadaccumulators having dry storagable charged electrode plates comprisingpolymerizing acrylic acid, methacrylic acid or amides thereof insolution with cross-linking agents, grinding the resultant gel, dryingthe ground gel and thereafter soaking the resin particles therebyobtained in concentrated sulfuric acid.

ABSTRACT 14 Claims, No Drawings METHOD OF PRODUCING A GEL CONTAININGCONCENTRATED SULFURIC ACID This application is a continuation-in-part ofapplication Ser. No. 16,931, filed Mar. 5, 1970, now abandoned.

This invention relates to a process of preparing agel containingconcentrated sulfuric acid for use in lead accumulators having drystoragable charged electrode plates.

From the time when lead accumulators provided with dry chargedstoragable electrodes have been introduced into the art, variousproposals have been advanced for overcoming the disadvantage associatedtherewith in that for setting the accumulator into operation, the samemust be filled with sulfuric acid, this making it almost impossible toprovide and marketthe accumulator together with the electrolyte.Proposals have been made whereby the accumulator is broughtto theoperable state, i.e., provided with the required sulfuric acid in thenecessary concentrated form merely by filling the same with water.

For example, it has been proposed to erect on the lead accumulator aplastic container of similar shape which contains the needed dilutesulfuric acid and which is filled into the accumulator for activation.Such arrangement of the accumulator and'electrolyte container have,however, the disadvantage that considerable space is required therefor.

It has also been proposed to provide the sulfuric acid in a concentratedand fixed form on the housing bottom so that the accumulator can be setinto operation merely by the addition of water thereto..

According to a further proposal, the concentrated sulfuric acid isstored in a locked synthetic plastic container arranged over the cellblock in the accumulator. The container is made of a synthetic resin notsubject to attack by the sulfuric acid but which resin is soluble inorganic solvents. Above this container there is arranged a furthersealed container containing an organic solvent. The second container ismade up of a watersoluble material. When water is introduced in theaccumulator, the container containing the organic solvent is destroyed,the organic solvent thus freed dissolves the sulfuric acid container andthe concentrated sulfuric acid is liberated and mixed with the water.Such an arrangement is quite complicated and not very reliable.

Heretofore, the known solid electrolytes have been prepared by utilizingpectin and the like in their manufacture and have proved unsuitablebecause of the resultant great space requirements. Concentrated sulfuricacid cannot be solidified by means of the known organic thickeningagents as these are attacked by concentrated sulfuric acid and do notform any gels therewith. The known inorganic thickening agents are alsonot suitable as these must beused in essentially greater amounts, andfurther, they give rise to an increase in the temperature during theactivation which produces results that are detrimental.

An object of the invention is a process for preparing a gel containingsulfuric acid that can be easily introduced into the accumulator andwhich will easily liberate its concentrated sulfuric acid content.

Another object of the invention is a solid sulfuric acid containingelectrolyte suitable for use in a lead accumulator provided with drystoragable charged electrode plates.

Still another object of the invention is a solid sulfuric acidcontaining electrolyte suitable for use in a lead accumulator providedwith dry storagable charged electrode plates which can be easily andeconomically produced.

A further object of the invention is a lead accumulator having drystoragable charged electrode plates and a solid sulfuric acid containingelectrolyte which can be easily activated.

These and other objects and advantages are attained in accordance withthe invention by providing a process for the manufacture of a gelcontaining concentrated sulfuric acid. The new process is characterizedin that acrylic acid, methacrylic acid or their amides are polymerizedin aqueous solution with a crosslinking agent, the thusly obtained gelground'up into particles and driedand concentrated sulfuric acid thenpoured over the dried gel particles.

An especially. rapid and excellent swellable material is ob'tained whenthe polymerization is carried out in sulfuric acid and by grinding therecovered gel, washing the ground'gelwith water, and then drying thesame. The particle size is of the resultant resin from 1 to 5 mm andpreferably amounts to about 3 mm. The smaller particle size, the fasteris the activation of the cell or battery.

As cross-linking agentmethylene bis acrylamide has proved particularlysuitable although other linking agents including acrylic-acid-allylester, methacrylic acid allyl ester, cyanic acid triallyl ester,ethylene glycol dimethacrylate can be usedin the polymerization.

For the polymerization, solution polymeriz ations catalysts such asperoxides, perborates and persulfates, for instance ammonium persulfate,have proved particularly suitable.

In accordance with the invention 3-8 weight percent, preferably 4-5weight percent of the organic material is present in the concentratedsulfuric acid, that is, in the sulfuric acid having a concentration ofover weight percent and preferably of -97 weight percent. This isachieved by pouring the concentrated sulfuric acid over the resinparticles to produce a product composed of sulfuric acid having aconcentration of at least 90 weight percent containing 3-8 weightpercent, preferably 4-5 weight percent of the polymer.

Particularly favorably fine particles of sulfuric acid gel are obtainedby drying the gelparticles after the first grinding, thereaftersubjecting the resin particles thereby obtained to a second grinding,and then treating the same with the concentrated sulfuric acid.

The mixture is allowed to swell by standing for about 72 hours and inthis form is filled into the accumulator.

The mass of swelled material is preferably arranged on a poroussynthetic foil disposed above the plate block and activated by thepouring on of water. In order to inhibit or prevent the admission ofmoisture, i.e., humidity, to the cell, during storage, the accumulatormust be sealed airtight.

The following examples are given for the purpose of illustrating theinvention and in no wise to be construed as limiting the scope thereof.

Example 1 5.0 g acrylic acid and 0.3 g methylene bis acrylamide weredissolved in 95 g water. Thereafter 0.05 g ammonium persulfate wereintroduced and the solution polymerized at a temperature of 80C forabout 10-20 minutes. The gel thus obtained was ground and the particleswere washed with water to remove low molecular weight water solublematerials therefrom and the washed particles dried at 100C. After thedrying the resin particles were reground so that they had a maximum sizeof 3 mm. 96 percent sulfuric acid was poured over the syntheticparticles so that the resin content in the sulfuric acid amounted to 4wt. After 72 hours of swelling, the solidified acid was layered onto aporous polyethylene foil. After thegel had been filled into the battery,it was sealed airtight.

In order to activate the battery, pure water was poured into the celland into the gel up to a previously indicated measuring mark.

Example 2 Example 3 5.0 g acrylic acidamide and 0.5 g methylene bisacrylamide were dissolved in g water and following the addition of 0.05g ammonium persulfate polymerized at about 60C for about 20 minutes, andfurther worked up as set out in Example 1.

Example 4 5.0 g acrylic acid and 1.0 g methylene bis acrylamide I weredissolved in 94 g of 80 percent sulfuric acid and the solutionpolymerized at 70C for about 10-15 minutes. The gel thereby obtained wasground, washed several times with water, dried and reground until theparticles did not exceed 3 mm in size. 96 percent sulfuric acid was thenpoured over the resin particles so that the content of the resin in thesulfuric acid amounted to 3 The essential advantage of the process ofthe invention lies in that sulfuric acid having a concentration of over90 weight percent can be brought into solid form and particularly intothe form of small particles of gel. The gel can be substantially freedof water soluble components which lessen the effects of the current. Theground and finished particles, i.e., concentrated sulfuric acidcontaining gel must be introduced into the battery under conditionsexcluding the presence of moisture. The resultant gel particles,however, having very small diameters, result in a very rapid activationof the cles thereby obtained.

2. Method according to claim 1, wherein said polymerization is carriedout in aqueous solution.

3. Method according to claim 1, wherein said polymerization is carriedout in a solution of sulfuric acid.

4. Method according to claim 1, wherein said polymerization is carriedout with methylene bis acrylamide as cross-linking agent.

5. Method according to claim 1, wherein said resin particles are soakedwith sulfuric acid having a concentration of at least percent by weightso that the resin content in the sulfuric acid amounts to 3-8 weightpercent.

6. Method according to claim 5 wherein said resin particles are soakedwith sulfuric acid so that the resin content in the sulfuric acidamounts to 4-5 weight percent.

7. method according to claim 5, wherein said sulfuric acid has aconcentration of from -97 percent.

8. Method according to claim 1, wherein said polymerization is carriedout with a catalyst selected from the group consisting of peroxides andpersulfates.

9. Method according to claim 1, wherein said polymerization is carriedout with ammonium persulfate as catalyst.

10. Method according to claim 1, wherein said resin particles are groundat least one further time before said concentrated sulfuric acid ispoured thereover.

11. Method according to claim 1, wherein said group member is acrylicacid.

12. Method according to claim 1, wherein said group member ismethacrylic acid.

13. Method according to claim 1, wherein said group member is acrylicacid amide.

14. Method according to claim 1 wherein said polymerization is carriedout with methylene bisacrylamide as unsaturated cross-linkable compound.

2. Method according to claim 1, wherein said polymerization is carriedout in aqueous solution.
 3. Method according to claim 1, wherein saidpolymerization is carried out in a solution of sulfuric acid.
 4. Methodaccording to claim 1, wherein said polymerization is carried out withmethylene bis acrylamide as cross-linking agent.
 5. Method according toclaim 1, wherein said resin particles are soaked with sulfuric acidhaving a concentration of at least 90 percent by weight so that theresin content in the sulfuric acid amounts to 3-8 weight percent. 6.Method according to claim 5 wherein said resin particles are soaked withsulfuric acid so that the resin content in the sulfuric acid amounts to4-5 weight percent.
 7. method according to claim 5, wherein saidsulfuric acid has a concentration of from 95-97 percent.
 8. Methodaccording to claim 1, wherein said polymerization is carried out with acatalyst selecteD from the group consisting of peroxides andpersulfates.
 9. Method according to claim 1, wherein said polymerizationis carried out with ammonium persulfate as catalyst.
 10. Methodaccording to claim 1, wherein said resin particles are ground at leastone further time before said concentrated sulfuric acid is pouredthereover.
 11. Method according to claim 1, wherein said group member isacrylic acid.
 12. Method according to claim 1, wherein said group memberis methacrylic acid.
 13. Method according to claim 1, wherein said groupmember is acrylic acid amide.
 14. Method according to claim 1 whereinsaid polymerization is carried out with methylene bis-acrylamide asunsaturated cross-linkable compound.